No, you don't capture the butterflies. You collect their milk by milking them either by hand or with a milker. My confusion was over how to use the milker when the whole world was still young.
It depends on your animal kinship skills. In the beginning, yes, you need lotion-- otherwise you just annoy the butterflies. You need to massage the butterfly first before you can milk it.
As you climb up the animal kinship skills ladder:
at some point you will no longer need lotion before you massage,
then no longer need to massage before milking,
then, once you acquire remote herdkeeping, you will be able to collect with the milker (you will still be able to milk by hand too).
So a sequence of milking skills which starts with needing lotion and massaging, and which ends with no longer needing lotion or massaging.